Summary
The axial skeletal rod of Veretillum cynomorium consists of a fibrillar collagenous matrix calcified with calcite. The present paper describes ultrastructural and crystallographic details of its organization and deposition.
At the inferior end of the rod is a calcification gradient between the noncalcified tip and the rest of the axis. Initial mineral deposits, which are sometimes associated with cell debris, give rise to calcitic nodules which enlarge by the radial growth of several lobes. These nodules fuse and form the core of the axis. Subsequent increase in diameter of the rod involves the radial development of irregular columns of calcite which arise from the peripheral nodules. Mineral surfaces exhibit a distinctive microarchitecture which can be related to the predominantly c-axis parallel growth of the calcite. Particular attention is paid to the relationship between mineral and matrix. The collagen fibrils, embedded in the calcite but never impregnated with it, are not responsible for the initial nucleation of mineral. The crystallographic orientation of the calcite also appears to be independent of these fibrils.
Résumé
L'axe squelettique de Veretillum cynomorium se compose d'une matrice fibrillaire de nature collagène, minéralisée par de la calcite. Le présent article fournit des données ultrastructurales et cristallographiques quant à l'organisation de cette structure et au dépôt du minéral dans la matrice.
La pointe inférieure de l'axe constitue un gradient de calcification entre l'extrémité non minéralisée et le corps entièrement calcifié. Les dépôts initiaux de calcite, parfois associés à des débris cellulaires, donnent naissance à des nodules qui s'accroissent de façon rayonnée, par bourgeonnement de plusieurs lobes. Ces nodules fusionnent et forment le coeur de l'axe dont la croissance ultérieure en diamètre, se réalise par le développement de colonnes irrégulières de calcite à partir des nodules externes du coeur. Les surfaces minéralisées présentent une microarchitecture qui peut être reliée aux axes cristallographiques de la calcite. Les relations entre le minéral et la matrice ont particulièrement retenues notre attention. Les fibres de collagène, enrobées par la calcite et non imprégnées par elle, n'interviennent jamais comme initiateur de nucléation du minéral. L'orientation cristallographique ultérieure de la calcite est aussi totalement indépendante de la matrice.
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Ledger, P.W., Franc, S. Calcification of the collagenous axial skeleton of Veretillum cynomorium pall. (cnidaria: pennatulacea). Cell Tissue Res. 192, 249–266 (1978). https://doi.org/10.1007/BF00220743
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DOI: https://doi.org/10.1007/BF00220743